1. Field of the Disclosure
The present invention relates to a laser module, and more particularly, to the laser module that uses an optical system to converge a group of laser beams radiated from a plurality of independent laser diodes into a resultant laser beam coupled into an optical fiber.
2. Prior Art
High-power and high-brightness semiconductor laser sources which have high efficiency are desirable for a variety of applications including machining operations such as cutting and welding, as well as optically pumping other lasers. Current high-power diode laser sources are somewhat limited in their intrinsic properties, such as the insufficient brightness and power of their output beams at least for certain laser geometries. For example, prior methods of pumping small-diameter rod lasers required the use of specialized and expensive optics to obtain reasonable coupling efficiencies.
One of the known configurations of a laser module that may have several applications includes an individual diode-lasers (edge-emitting semiconductor-lasers) providing an efficient source of relatively bright light. Light is emitted from an aperture that has, for example, a height of between about 1.0 micrometers (.mu.m) and 2.0 .mu.m and a width depending on the output power required from the individual diode laser with the width being greater the greater the power required. This width can be as large as few hundreds micrometers. The height and width directions of the emitting aperture are usually termed the fast and slow axes, respectively, by practitioners of the art. The quality of a beam emitted from a diode-laser is high in the fast-axis direction but low in the slow-axis direction, with the slow-axis quality being lower the wider the aperture.
An individual diode-laser of the known prior art typically does not emit sufficient power for the applications being considered here. When more power is required than one diode-laser can supply, it is a usual commercial practice to provide a linear diode-laser array, commonly referred to as a diode-laser bar. In such an array, a plurality of diode-lasers (emitters) are formed on a single substrate (the “bar”) so that the emitting apertures of the emitters are aligned in the slow axis direction. The light from all of the emitters must be collected by an optical system of some kind and focused on material to be processed. Such a system requires a complicated arrangement of cylindrical and circular lens elements. Further, the emitters, being on a common substrate, must be connected electrically in parallel. This creates a requirement for a high-current power supply. The cost of such power supplies rises in proportion to the deliverable current.
With the advent of relevant technologies, individual laser diodes have become more powerful. Yet, the power produced by even the most sophisticated individual laser cannot adequately address the needs for the above-discussed applications.
FIG. 1 illustrates a laser diode module 10 disclosed in copending application Ser. No. 12/215,327 which is incorporated herein in its entirety. The module is provided with a few individual laser diodes 4. Each of laser diodes 4 is associated with a group of optical elements including fast- and slow-axis lenses 6, 8, respectively and a deflecting mirror 5. The laser diodes 4 with respective groups of optical components are mounted to a housing 2 in a step-wise manner one above the other to produce three parallel light beams which are collected by an objective lens 7. The objective lens is configured to couple the light from all three into an optical fiber 9. The power produced by the module is relatively high while the module has a space-effective structure.
Still the power demands in certain applications cannot be met by the above discussed structure. The increase of the output power of the module by increasing the number of diodes is the subject of trade-off: the more diodes the bulkier and longer the module. Considering the demand for smaller structures, this solution does not seem to be practical.
Accordingly, a need exists for powerful laser diode modules overcoming the above-discussed limitations of the known laser diode modules.